aLegendWai: A sgf file for this example is provided by me. It has more variations and comments. I hope it can illustrate better for all of the following.
Click on http://hk.geocities.com/wai_wai_sir/my_go_q/stop_en_run.zip to download.
To know how to open and view sgf file, see: http://hk.geocities.com/wai_wai_sir/htm_sub/frameset.htm (click on FAQ)
Black 3 is a powerful play as it shuts White into the corner. White cannot counter Black 3.
Black captures the marked stones and kills the corner as well. As Black 3 in the diagram above is such a powerful play, White has actually made a mistake before and should have extended to Black 1 above herself.
Add more examples if you feel like it :o) --ArnoHollosi
aLegendWai (9k? KGS): The above is just part of the story.
It depends on the situation.
If a ladder is favorable to B, playing at b will be observed.
Otherwise, a.
Even if the ladder is favorable to B, it doesn't mean W should not play in this way. is used as a threat to B. When a W ladder breaker occurs, B has to capture the W stone. Otherwise you should know what to do ^^
Scartol: Well, I tried to play through the possibilities for the following question, but because of my difficulty reading, I couldn't sort it out.
Suppose White plays at 1 here, instead of a. Can Black still kill the corner?
aLegendWai(9K? KGS): W should play at instead. Playing at 1 leaves B a chance to play useful atari.
W already live without .
Jan: I think the idea of the original double hane is not to kill White, but to prevent White from escaping. If Black omits 3 in the original diagram, White could later play 4 or a in the following one, for a substantial gain in territory. Your White 1 lets Black make a trumpet connection with very good thickness.
Hans: Depending on the white stones in the neighbourhood normally black should connect at a in the diagram above. Since the six white stones are very strong white cannot cut and white has only one point for playing a peep. Opinions?
aLegendWai(9K? KGS): It is my little opinion. Solid connection or trumpet connection is possible depending on whole-board situation.
The weakness at "a" occurs when W has a ladder breaker. Then 2 groups are separate. It doesn't automatically mean the solid connection is very wrong however. In my opinion, I think it is genereally better than the trumpet connection
The weaknesses of peep at "a" and "b" can force B in lump shape. However it is not necessarily mean B must connect when there's a peep.
W's peep at A
If whole board situation favors, when W's peep at A, black may choose to play at for a trick play. And force W into confusing fight. At that time, B can keep W running and build another strong wall or influence
Note: The line of play may not be optimal. It is just to show you roughly about the idea.
W's peep at B
If whole board situation favors, when W's peep at B, black may choose to play at D. Even if W cut at , B will treat
lightly and force W to capture it. A more horrendous wall is built.
However W is able to escape. But as I said previously, the whole-board situation may justify B to play like that (eg there're some B stones around before W peeps, so W can't really gain much from the escape).
Any comment is welcome.